Uncertainty and response time instability can affect invoked Web services' usability, performance, trustworthiness, and dependability. To resolve uncertainty, researchers have applied a three-pronged approach. First, they remove uncertainty through advances in data collection, response time measurement, and benchmarking. Second, they employ a mathematical foundation for modeling uncertainty. Finally, they improve fault-tolerance techniques by making well-considered choices of time-outs and trade-offs between cost, availability, trustworthiness, and performance.